Abstract: A hang-on device mounting structure for securing a hang-on device to a motorcycle or bicycle to avoid interference of the hang-on device with the vehicle rider is disclosed to include one or multiple base panels mounted in a toolbox or luggage-carrier of a motorcycle or bicycle, each base panel having one or a number of positioning units, and one of a number of connection devices for securing a hang-on device to the base panel(s), each connection device has a mounting member for fastening to one positioning unit of one base panel, a connector connectable to one matching connector of the hang-on device and an extension member connected between the mounting member and the connector.